What kind of beasts are you interested in? Scary beasts to menace the player characters when they're out in the wilderness? Annoying beasts to tribble up their ship? Food beasts to dress up the dinner plate? Game beasts to hunt on safari? Beasts of burden to use when tribbles eat the power cables on the air/raft?

Thanks for the input. Really looking for things that could be used for animal handling...mounts, guard/police "dogs", pets. Animal Handling skill is pretty useless without animals to handle. Maybe I will have to do some world research and design some beasts and publish for the community.

If you need a creature, first look at the animal encounters chart (classic Book 3, my Mongoose books are put away during my seemingly endless home renovations so I'm not sure where they are there) and pick animal types that fit your needs.

So, I'll make up a watch beast.

Rather than a carnivorous chaser domesticated into an often sedentary omnivore, how about a more alien creature? Here's something I came up with while driving on morning errands:

The "spider cat" is neither a spider nor a cat. It isn't even biochemically related to Terran life. It is a ten legged creature about the size of a small house cat, with curly fur made mostly of carbohydrate (that feels like scratchy cotton). Adults mostly feed in small family herds as grazers, eating plants and incidental tiny animals.

When unrelated herds meet they form mating parties, each pairing with a member of the other family. Pairs lie in wait as pouncers, watching for prey for their larvae. When they spot suitable prey, they pounce and inject the larval prey with a venom that makes them lethargic and induces early molting. While the prey are lethargic, they lay pairs of eggs in the proximal joints of the prey animal's legs; the eggs pairs merge, genetically conjugate, and develop into larvae.

When the prey animals molt, the larvae crawl to the body of the prey and burrow into its skin and feed on the under-skin nutrient stores until the next molt, when they emerge as juvenile adults, about the size of large mice. Each group from an individual prey animal remains together as a family herd, and switches to the grazer feeding pattern until they are large enough to mate.

Their favored prey animal is the "ten-cow". Their life cycle is similar, but their eggs are laid in the decomposing vegetation that their larvae eat. A well fed ten-cow usually survives a spider cat breeding cycle, but it is more susceptible to disease.

The domesticated spider cat eats more as a grazer, and has much more frequent breeding cycles, so they have the alertness of pouncers all the time. They often lay eggs on unsuitable prey, but can reproduce by laying eggs in vegetation supplemented with animal nutrients. Commercial spider cat chow is widely available on worlds where domesticated spider cats are kept; spider cat larva chow is also available, but genetally requires refrigeration.

Spider cat venom is a hallucinogen to most Terran-biology mammals, mildly for Vargr, powerful for humans. It is a moderate skin irritant to Aslan and K'kree, a low-quality nutrient to Droyne (and their close relatives, Chirpers), and apparently inert to Hivers. Spider cat eggs do not develop into larvae without biologically compatible food sources, but they are skin irritants to most life forms.

So there you have a complete alien animal, and hints of a complete alien biology.

It's a MgT 1e Supplement geared towards creating alien races for NPC/PC use but it's also very cool for creating alien beasties as well.

It can be very detailed or you can skip a few steps that deal with sentience and get a very cool and possibly even 'realistic' lifeform. And as steve98052 mentions above, the creature could form the basis of an entire biosphere... highly recommended.

And thanks to rust (rust2 now?...) for initially posting such a cool idea!